Continuously manufactured products, can include profile shapes and web materials. Profile shapes may take many forms such as tubing, hose, pipe, and plastic lumber with dimensions such as 2×4's and 4×4's, while web materials are typically a continuous sheet of material of a given width. Profiled shaped materials can be any shape, but are usually elongated products with cross-sections that are generally square, rectangular, or circular. Looking down the length of the product, the profile shape can have four walls that define a square (or rectangle), with a hollow center. The opposing walls generally will have equal cross sectional lengths and each wall will usually have an equal thickness measured from the inside surface of the wall to the outside surface or outer periphery of the wall.
For example, 4×4 extruded polymer lumber may be of any length, but the width and depth are generally both 4 inches, measured about the perimeter. Thus, the product has four sides that are all equal in length (hence 4×4), and each side has a thickness (which is generally uniform for all the walls).
A continuously formed product with a shaped profile generally begins in liquid form (or amorphous solid) as a result of heating in an extruder. The raw material is introduced to the extruder in pellet form. An exit orifice of the extruder includes a center shape called a mandrel and an adjustable outer ring called a die. These two objects can have a discernable space between them and the extruder injects the liquefied product material through the space. When the liquefied product is properly cooled, it can form a desired shape of the final work product. The mandrel can define the inner walls of the product and the die can define the outer walls of the product. As the desired shape is acquired, the amorphous solid material can be sent into a cooler for hardening.
The work product can move through these operations by use of a pulling device. The pulling device can be located toward the end of the manufacturing process, and can pull the hardened product down the processing line. One concern in this process is maintaining a desired shape and wall thickness for each side of the product. Wall thickness can be increased or decreased by changing the speed of the pulling device. Similar to stretching a piece of bubble gum, by increasing the speed of the pulling device, the amorphous portion of the product will typically stretch, thereby reducing the wall thickness of the final product. Alternatively, slowing the pulling device speed can increase the wall thickness of the final product.
While the pulling device has the ability to increase or decrease the wall thickness by changing speed, a pulling device can generally only simultaneously change the thickness of all sides of the product. Therefore, if one side has an appropriate thickness, but another side does not, the pulling device will generally be of little value. Similarly, measuring the wall thickness can be a difficult task, as many measuring devices require contact with the product, and others do not provide accurate readings.
Web materials can be made of any of a plurality of materials including paper, plastic, carpet, or other materials. Web materials (as well as shaped profiles) may have a plurality of different components that need measurement and adjustment for quality control and cost management. These components can include length control, width control, wall thickness control, coating thickness control, film thickness control, and opacity control.
Historically, nuclear measurement devices, ultra sonic sensors have provided measurement and control of the dimensions of continuously formed work products such as web materials and shaped profiles. While these techniques can have benefits, they also have drawbacks. With shaped profiles, this measurement is generally taken on cylindrical pipe and some non-cylindrical tubing because of the symmetry of the products. Shaped profiled work products that have sharp angles and several sides, such as continuously formed lumber products, do not easily lend themselves to sensors that usually contact the product to measure wall thickness. Using a single sensor to measure wall thickness of any multisided object usually can be unreliable. In addition, contact by the sensor against the surface of the product has the potential to alter the position or shape of the product, thus decreasing the sensor's accuracy.
Additionally, there is often difficulty in the manufacturing process due to misplacement of the die with respect to the mandrel. This can result in varying wall thickness of each side of the work product. As stated above, work products having continuously manufactured walls of different thickness usually renders the pulling device unable to effectively correct wall thickness errors.
Further, additional problems can occur during other types of production activities. With continuously manufactured products, such as sheet materials and shaped profiles, defects may exist on the material during manufacture. The defects can occur in any of a variety of ways including dimension defects, coating thickness defects, film thickness defects, and opacity defects. One problem that exists is locating the irregularity of the work product so that a correction to the production process can be made
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.